Amplifier



June 29 1926. 1,590,263

J.. s. STONE AMPLIFIER Filed Jan. 4, 1923 I 2 Sheets-Sheet 1 2 AIIIIIIF v Z;

IN VEN TOR W TTORNE Y Jam 29 1926.

J. s. STONE AMPLIFIER Filed Jan. 4, 1.923 2 Sheets-Sheet 2 v INVENTOR (fr/412 622/46 J7me ATTORNEY Patented June 29, 1926.

UNITED STATES PATENT OFFICE.

JOHN STONE STONE, OF SAN DIEGO, CALIFORNIA, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

AMPLIFIER.

Application filed January 4, 1923. Serial No. 610,608.

The to provide a new and improved distortionless amplifier for variable electric currents.

Another object of my invention is to com- 6 bine transforming or amplifying units, each with a non-linear characteristic relation between input 'and' output, in a system that shall give a linear characteristic. Anotherobjeet of my invention is to combine ther- '10 mionic vacuum tubes in a system that shall invention is defined in the appended claims.

Referring to the drawings, Figure 1 is a circuit diagram showing one embodiment of my invention; Figs 2, 3 and 4 show modifications; and Figs. 5, 6 and 7 are characteristic diagrams.

Fig. 1 shows a system employing a twoeleetrode thermionic vacuum tube T and a three-electrode thermionic vacuum tube T An input electromotive force E is indicated as having the direct component E and the small superposed alternating component 6. The output current I flows through the external resistance 1- Other elements of Fig. 1 and their relation to one another will be readily apparent from the drawing, in connection with the following description of the manner of operation of the system.

It is known from experiment with a large number of tubes that the current and voltage across the electrodes of a two electrode tube have the relation that the current varies ap-v principal object of my invention is Accordingly, by the square law just referred to,

where 0: is a constant. It is assumed that the battery E has its negative pole connected to the grid of the tube T and that the electromotive force of this battery E is a so high that the grid is always negative, and hence no appreciable current flows in the circuit ofthe battery E Accordingly, the current through the tube T is the current I through the battery E It follows that E=rI+ (2) Solving as a quadratic for we get the result For the tube T general square law has been established experimentally which is embodied in the following equation for the. tube T E 2 I =o[M+E -ie} (5) that is, the plate current varies as the s uare of a function of the plate voltage an the grid voltage. ,u is a constant depending on the design of the tube and e is a small electromotive force corresponding to the intrinsic potential difference between the filament and the system constituted by the grid and plate. Substituting from equation .(3)

to equation (4) and then from equation (4) to equation (5), we get then equation (6) will reduce to %(1 +4a rE) 111 10 1 +2 This shows that the output plate currentfor the system stands inlinear relation with the inputvoltage E.

This is an equation between two variables I;-

It is well known that with a single tube the relation between output and input is, in eneral, non-linear. This means that ampli. cation'will be accomplished only with distortion.

Referring to Fig. 5, the curve A exhibits the relation between voltage E and, current I'for a two-electrode tube. If the current is made to vary linearl with the time in the manner indicated bytlie diagram at B, the voltage will vary in the manner shown at C, whose points are found by projecting from ,the diagram B on the curve A and then the curve A to the curve C, keeping the time intervals uniform. It will be noticed that the diagram B is made up of straight line segments and that the corresponding lines in G are curve; thus the distortion is exhibited. Y

Referrin to Fi 6, this shows a diagram for the re ation and equivalent voltage E for a three-electrode tube, where Assuming that the voltage E varies in relation to time, as indicated by the diagram at B, the correspondin variation of the output current I is given y the curve at O. The departure from linearity in curve C indicates the distortion.

Figs. 5 and 6 are combined in Fig. 7, which From the square law itTollowsthat tween output current I from that 0 is tapped at an intermediate point with the 95 shows the operation of the-device according to Fig. 1. If the current I of Fig. 1 varies in time according to the diagram B, then the output electromotive force super osed on battery E across the filament an grid of tube T, will vary accordin to the curve C. This electromotive force is a linear component of E as shown by equation 8*), and the output current I, will be foun by 00 projecting from curve C to A and thence to C. Notwithstanding the curvature of diagram C, the straight line diagram B transforms through C to the straight line diagram 0', indicating absence of distortiqn between in ut and ultimate output. arious measures have been tried and adopted to remedy the defect due to distortion in a single tube, as shown by Fig. 5 I or Fig. 6. One plan depends on the fact that although the output characteristic is curved, if it is worked over a narrow range the portion of the. characteristic involved will be short and nearly straight. Another expedient is to employ a large external re sistance in the plate circuit, which makes the characteristic more nearlf straight. By my invention. it is accom ished that the characteristic will be ma e straight as in v Fig. 7, if two tubes be employed according 30 to the plan outlined in connection with Fig.

.1. The demonstration here given has involved the square law, but a review of the foregoing steps shows that the result may be made the same for a more general finite as continuous, .single valued functional relation, that is a linear relation would be obtained between the input electromotive force and the output current. -In the following further examples of my invention, I employ the square law only by way of example for the more general relation.

In Fig. 2 a s stem is shown' which differs f it g. 1 in that the resistance r part 1' next to the tube T as shown. Moreover, in this case r, is not assumed to be negligible.

. By a series of steps that parallel those taken for the case of Fig. 1, it may be deguced that in Fig. 2 the voltage E. is'given l and E. Let us assume tentatively that the rational and irrational parts can be equated equations will reduce to Hence we may say that imposing the condi-J ditions of equations (14) and lishes the linear relation (11) etween E and I Evidently by proper design and adj u'stment, equations ('14) and (15) can be established. Thus we see that in the system of Fig. 2,witho,ut neglecting m, it the adjustments are made to satisfy equations (14) and (15) then the output current I, depends linearly on the input voltage E. It will be seenthat Fig. 1 1s aspecial case of Fig. 2 in which vr zO; this condition necessitates the condition that 13:0, thus re- 15) estabducing the value E7 to Y 2(117 In Figs. 1 and 2 theinput voltage has been applied first to the two-electrode tube output volta e E, and the input voltage and the output current has been taken from the three-electrode'tube. In Fig. 3 the order is reversed. Here the .plate current is' aner-Nat) whence Accordingly, thepotential difierence across E If on is sma compared to 0:, equation (183 indicates amplification of potential without distortion.

In Fig, 4there is illustrated a more gen-. eral form of the circuit arrangements in which the inherent. distortion of the audion amplifier is neutralized by the use of three tubes, in a sense combining the principle of Fig. 1 and the principle of Fig. 3. It is believed that a mathematical discussion will not be necessary for this case, having been sufliciently presented in connection with the earlier cases.

Fig. 4 shows explicitly that the kind of distortion produced by the audion amplifier may be neutralized at any remote polnt in the transmission line by the system here disclosed, because the resistance r -may represent the resistance of a transmission line.

I claim:

' 1. In combination, a two-electrode vacuum tube anda three-electrode vacuum tube,

the terminals of the two-electrode tube being connected with the in ut terminals of the three-electrode tube, t e circuits and their impedances being adjusted so that the output and input of the combination are in simpler linear relation.

2. In combination, two thermionic vacuum tubes, each with a non-linear characteristic and each with associated conductors forming a pair of input terminals and a pair of output terminals and means connecting the output of one tube with the input of the other, the combination being designed and adjusted so that the ultimate output shall be in linear relation with the initial input.

3. In combination, two thermionic vacuum tubes, each with a filament-cathode and a plate anode, one of said tubes also having 7 a grid, said tubes having two terminals'of one connected respectively with the two terminals of the other and having their circuit elements "designed and adjusted mutually to compensate their distortion whereby the ultimate output of the combination will be undistorted in relation to the initial input.

4. In combination, a two-electrode tube with a resistance 1' comprised in its input circuit and with a portion. nthereof comprised in its output circuit, a battery of electromotive force E in said output circuit, a

three-electrode tube having its in ut con-.

nected in said output circuit and aving a resistance 1' and a battery of electromotive force E com rised in its output circuit subject to the esign equations where- (and a are constants for the threeelectrode tube and a is a constant for the two-electrode tube.

V 5. In combination, a two-electrode tube with a. resistance r comprised in its input circuit and with a portion r thereof comprised in its output circuit, a battery E; in its output circuit, a three-electrode tube having lts input connected in said output and having a resistance 1' and a battery of electromotive force E comprised in its output circuit, the said resistances and electromotive forces being so proportioned in relation -to the constants of. the saidtubes that the curvature of the volt ampere characteristic of one tube compensates for such curvature l,

of the other tube and gives an'over-all linear JOHN STONE STONE. 

